Why headline figures can mislead
Solar articles and proposals often present one system cost, one annual saving and one payback period. Those figures can be useful, but they depend on assumptions that need to be visible. Generation, self-consumption, tariffs, export value and finance costs can all change the outcome.
What makes up the installed cost
- Panels and mounting equipment.
- Inverter, monitoring and electrical protection.
- Cabling, isolation, testing and commissioning.
- Scaffolding, access and site logistics.
- Any roof, structural, electrical or network work outside the standard scope.
- Optional battery storage, backup equipment or smart controls.
The four numbers behind savings
Most savings estimates are built from annual generation, self-consumption, avoided import value and export value. If these numbers are not shown, the homeowner cannot easily test or compare the proposal.
How export fits in
The Smart Export Guarantee can provide payments for eligible exported electricity, subject to supplier terms and scheme criteria. Export income should be separated from the value of electricity used on site. A high export assumption should be checked against current supplier terms.
Use scenarios, not a single promise
- Central case: reasonable property-specific assumptions.
- Cautious case: lower generation, lower self-use or lower export rate.
- Improved-use case: realistic behaviour changes such as shifting flexible demand into daylight hours.
Questions to ask before deciding
- Is the total price itemised and clear?
- What generation figure is being used and how was it calculated?
- What self-consumption percentage is assumed?
- Which import and export values are used?
- Are maintenance, replacement, finance or battery assumptions included where relevant?
- Can the provider show a cautious scenario as well as the headline case?
Permissions and connection applications carry their own time cost, and some carry a fee. Which of them apply to a given property is covered in planning permission, Building Regulations and grid connection.
Information and source control
Information correct as of: 17 July 2026
Sources available on request or reviewed during consultation.
